1. Field of the Invention
The present invention relates to an organic light emitting device and a method of manufacturing the organic light emitting device, and more particularly, to an organic light emitting device including a transparent electrode having good ohmic contact characteristic and high transmittance and a method of manufacturing the organic light emitting device.
2. Description of the Related Art
Recently, in response to the government's low-carbon green growth policy stance, semiconductor illumination using LEDs (light emitting diodes) and OLEDs (organic light emitting diodes) as semiconductor light sources has attracted much attention. The semiconductor illumination is environment-friendly illumination which does not use hazardous substances such as mercury and lead, and the semiconductor illumination is also low-power-consumption illumination of which power efficiency is much higher than that of traditional illumination. In particular, unlike the LED as a point light source, the OLED has a structure of thin planar light source, so that it is possible to implement transparent and flexible illumination, which cannot be easily implemented in the traditional light sources.
In addition, since the OLED illumination as transparent, flexible illumination can be used for applications such as new-concept smart window illumination, portable rolled-up illumination like a scroll, and curtain illumination, the OLED illumination has been more actively researched.
However, in order for the OLED to be used for various applications, the problem of high driving voltage of the OLED caused by bad ohmic characteristic between a transparent electrode and an organic semiconductor layer needs to be solved. The driving voltage of the OLED is mainly determined by injection and movement of electric charges. Therefore, two characteristics of the injection and movement of electric charges need to be improved in order to improve the driving voltage.
Since the charge injection characteristic is determined by energy potential between the transparent electrode and the organic semiconductor layer, the ohmic contact is formed by reducing a difference in energy barrier between the transparent electrode and the organic semiconductor layer, so that the injection and movement of the electric charges can be effectively performed. Therefore, the OLED having a low driving voltage can be implemented.
However, in the current OLED, due to a large difference in work function between ITO (4.3 eV) mainly used for a transparent electrode and an organic semiconductor (6.3 eV), the ohmic characteristic is bad, so that there is a problem in that charge injection efficiency is low. In addition, since ITO has large transmission loss in a UV wavelength range, in the current organic UV-LED, there is a problem in that light extraction efficiency is low.
In order to solve the above-mentioned problems, the ITO used for a transparent electrode and the organic semiconductor are allowed to be ohmic contact with each other so that charge injection is efficiently performed. However, transmittance and conductivity of a transparent electrode currently generally used is in Trade-off relationship. Namely, since a material having high transmittance in a UV wavelength range has a large band gap, the conductivity thereof is too low to be used as an electrode, and since the material is not in ohmic contact with a semiconductor material, it is impossible to use the above material as an electrode.
In the related art, a transparent electrode having high transmittance with respect to light in a UV wavelength range as well in a visible wavelength range and high conductivity due to good ohmic contact cannot be implemented. Therefore, in order to implement OLEDs which can be applied to a UV wavelength range as well as a visible wavelength range, the transparent electrode having high transmittance and good ohmic contact with an organic semiconductor layer needs to be developed.